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  • Single Storey Extension Costs

    Trying to find out how much a new single storey extension costs to build? In this article we investigate the prices of different types of extension as well as the cost of hiring a builder to carry out the work.

    Average Cost of a Single Storey Extension:

    Depending on the complexity of the job, it usually takes: 11 – 13 weeks


    How Much Does a Single Storey Extension Cost?

    The cost of a single storey extension will largely depend on the size of the extension you choose to build. The next most relevant factor is the quality of the finish you go for. A small extension costs as little as £15,000. This would likely be a small side return extension with a basic finish.

    For a larger single storey extension, you could opt for a large wrap around extension with large amounts of glass in both the roof and walls. This could cost up to as much as £100,000.

    The average cost of a single storey extension is around £35,000. This would give you a good-sized rear or side extension and includes the cost of a kitchen, as this is the most common use for a single storey extension.

    Single Storey Extension Prices

    With all the costs included the biggest two factors that will affect your home extension cost are the number of square meters and the quality of the finish.

    Quality of finish Cost per m2
    Basic £1,000 - £1,700
    Good £1,700 - £1,900
    High £1,900 - £2,200

    Labour Costs and Timescales

    The labour costs and time scales will vary a great deal depending on exactly what work you have done in your extensions. The following sections should give you some rough estimates on average costs and timescales

    Timescale and Labour Cost Based on Type of Extension

    Type of Extension Duration Average Labour Costs
    Lean-to Rear 11 – 13 weeks £25,000 - £40,000
    Side Return 9 – 12 weeks £15,000 - £25,000
    Wrap Around 10 – 14 weeks £40,000 - £100,000
    Kitchen 10 – 14 weeks £25,000 - £100,000

    Cost Per Hour of Different Tradesmen

    Tradesman Average cost per hour
    Builder £20 - £35
    Tiler £20 - £40
    Plumber £35 - £45
    Electrician £50 - £120
    Plasterer £30 - £50
    Decorator £20 - £50
    Joiner £35 - £45
    Roofer £30 - £40
    Kitchen Fitter £20 - £30

    Supply Costs Only

    When calculating your extension costs, there are a lot of materials to consider. It is easy to see how final extension costs can add up quickly.


    Type Size (cm) Average Cost
    Velux 98 x 78 £325 - £375
    140 x 78 £400 - £450
    180 x 78 £500 -£550
    uPVC 60 x 90 £250 - £400
    90 x 120 £400 - £600
    120 x 120 £650 - £900


    Type Average Cost
    Internal £50 – £200
    External £300 - £500
    Patio £300 - £1,000


    Type Average cost per m2
    Vinyl £7 - £20
    Wood £17 - £70
    Carpet £4 - £40
    Tile £10 - £60


    Type of Heating Average Cost
    Traditional Radiator £60 - £150
    Electric Radiator £150 - £300
    Underfloor Heating £100 - £150 per m2
    Boiler £500 - £3,000


    Item Average Cost
    Units with Doors and Handles £3,200 - £5,500
    Worksurface £200 – £2,000
    Fridge £400 - £1,200
    Fridge-Freezer £600 - £800
    American Style Fridge £500 - £1,300
    Chest Freezer £160 - £500
    Gas Hob £100 - £500
    Induction Hob £300 - £900
    Ceramic Hob £150 - £300
    Single Oven £500 - £1,100
    Double Oven £400 - £1,200
    Dish Washer £400 - £1,000

    Bathroom Suite

    Fixture Average Cost
    Bath £80 - £500
    Shower £60 - £1,000
    Show enclosure £100 - £550
    Toilet £50 - £500
    Sink £50 - £300
    Taps £50 - £100


    Type of Lighting Average Cost
    Pendant/chandelier £40 - £100
    Simple ceiling or wall lamp £40 - £60
    Recessed Spotlights £80 - £110
    Dimmable ceiling or wall lights £80 - £100

    Additional Costs

    Whenever you get work done on your home, there are additional costs that can arise. This is especially true if you need to have a building control inspection. Here are some extra costs that you might not have considered.

    Skip Hire

    There will be rubble and waste created as part of the building work. The easiest way to dispose of this is with a skip. If skip hire is not included in your quote, you should add £250 - £450.

    New Boiler

    If you are adding plumbing to your extension for a bathroom or a kitchen, then you might need to get a new boiler. If your current boiler is working at full capacity, this is your only option. The average cost for a new boiler is £1,500 - £2,500

    House Rewire/New consumer unit

    When you get an extension built, you will be adding on to your existing electrical systems. This can bring to light issues with your current set up. In the most extreme case, you may need to a full house rewire. This can cost around £4,000.

    A more common issue is that you may need to update your consumer box. The average cost for this is £500.

    Removing Drains

    If your existing drains are in the way of your planned extension that you may need to move them to a new location. To check if this is needed you can have a drain survey carried out for around £250. If tour drains do need to be removed or relocated this will cost between £200 - £1,300.

    Underfloor Heating

    Underfloor heating is a fantastic heating option. Building an extension is a good opportunity to have it installed. The overall cost will depend on the area it is fitted under, but the average cost for installation is £800.

    Site Survey

    Before getting any major work, it is advisable to have a site survey completed. This involved getting a surveyor to have a close look at your property to identify any issues that already exist or might arise during work. Although it can cost £600 -£1,400 depending on the size of your home, it can save you money in the long run.


    An architect can draw up plans for your extension if you choose. This is not necessary for a single storey extension, but it can be helpful to keep the project on task. Plans usually cost 7-15% of the cost of the extension.

    Planning Application

    It costs £206 to apply for planning permission.

    Building Regulations

    To get your extension certified as meeting building regulation require paperwork and site visits. There is a cost for this. It varies from £500- £1,000 based on where you live, and the scope of the work done.


    If you are going to move out while the work is completed, then you need to check your home insurance. Your home may not be covered while you aren't in residence. In this case, you will need to get insurance to cover the building work. This should include employer's liability, public liability and construction cover. The average cost for this is £500 - £800.

    Cost Factors of Building a Single Storey Extension

    There are a few factors to bear in mind when you are setting your budget. The main factors that affect the cost of a single storey extension are the size and the finish. But there are other factors that it is worth keeping in mind while you are making your plans.

    Size of Extension

    When you are getting an extension on your home, the single biggest factor that will affect the cost of your extension is the size of it. The bigger the extension is, the more you will end up paying. If the area inside the extension is simple, with no internal walls, then this will lower the cost per m2 slightly. However, even with this in mind. The larger the area of your extension, the more you pay.

    Quality of Fixtures and Fitting

    After the size of the extension, the next biggest factor is the quality of the finish. Choosing high-end options can lead to the final price being more than double what it would be when choosing the basic options.


    Type of Extension

    The type of extension you choose will go a long way towards dictating how large your extension will be. Side return extensions create the smallest extra space so are often the cheapest option, while a wraparound kitchen extension will create the most space and have the most expensive fittings and fixtures.

    Expensive Groundworks Needed

    If it is difficult to dig the foundations and lay the footing for your extension, then this can increase the cost of your extensions. This might be the case if the ground is hard to work with. Debris in the ground can also raise the costs.

    Building Regulations

    In most cases, building regulations don't add a lot of cost to a building project. However, if you are building an extension onto an older home, there may be some unexpected costs. This is especially true if the home has not recently been updated. Building regulations will apply to your whole home, not just the extension. This can lead to the need for electrics to be looked at or door replaced.

    How to Build a Single Storey Extension

    There are a lot of factors that need to be coordinated when building an extension. Problems with scheduling or weather can cause small delays, which can have knock-on effects that throw the whole plan off by weeks. The following is an outline for a good size single storey extension, where everything goes to plan.

    Weeks 1-2

    The first two weeks are used to prepare the building site. The footings will be dug, and the foundations poured. Any drain work will be completed at this time.

    Weeks 3-4

    The all-important damp proof course will be installed at this point as well as the concrete base for the flooring. Some drain work may be finished off during this time.

    Week 5

    The external walls will be built. If you have a cavity wall, the insulation will go in as the walls are built. The new walls will be joined to the old as they go up.

    Week 6

    The internal walls will be constructed, and the cavity wall insulation finished.

    Weeks 6-7

    Whatever roof you have chosen the structure for it will be built now. Any roof windows will be framed at this point.

    Week 7

    Once the roof membrane is secured, your roofing of choice will be installed.

    Week 8

    The external doors and windows will be fitted. This will make the new extension watertight, allowing internal work to proceed.

    Week 9

    First fix will happen. This is basic plumbing and electrics. Some internal carpentry may be able to happen at this point as well.

    Week 10

    The extension will be joined to the existing house. This involved breaking through the old external wall.

    Week 11

    The plaster will go on the walls. It must be given time to go off, before work proceeds.

    Week 12

    All the exciting things happen now. The second fit electric and plumbing, bathrooms and kitchen and final trim are fitted, and you can lay the flooring.

    Can I Build a Single Storey Extension Myself?

    There are a lot of different skills required to build an extension. Unless you are a professional builder, then you are unlikely to be able to complete the whole job on your own. Even then you might need to hire an electrician or plumber to help with some more specialised jobs.


    If you want to bring down the cost of your single storey extension, then you can take on the jobs you feel confident about. Relatively easy jobs include laying floorings, hanging internal doors, and decorating. Any jobs you take on will help to reduce the average cost of your extension.

    If you do plan to take on any part of the work, you need to communicate this clearly to your project manager. This is usually the lead contractor. They need to schedule when all the work happens. If you are doing some of the work, they need to know as soon as possible. This is so they can plan the other work around you.

    Types of Single Storey Extension

    If you are extending your house by a single storey, then there are still a few ways to do this. The main options with their pros and cons are as follows

    Side Return Extension Cost


    A side return extension is an extension that uses the alleyways that run down the side of some houses. Many Victorian houses have these little alleyways down the sides that are often used to store bins. The average cost of a side return extension is £15,000 - £25,000.


    ✔ Quick to complete

    ✔ Doesn’t use garden space


    ✖ Only creates a small amount of space

    ✖ Not an option for all houses

    Lean-to Rear Extension Cost

    Lean-to extensions are usually a single room-sized extension to the rear of a property. The roof on these extensions is typically pitched, which is where the name comes from. A lean-to extension is a common choice for small extension. Costs are around £25,000 - £40,000.


    ✔ Lots of flexibility

    ✔Easy way to add a single room


    ✖ Not the cheapest option

    Wrap-a-round Extension Cost


    A wraparound extension is the combination of a rear and side extension. It makes a large effect on the downstairs space in your home. The average cost for this type of extension is £40,000 - £100,000.


    ✔ Creates a lot of extra living space

    ✔ Provides a lot of options


    ✖ Can be much more expensive

    Kitchen Extension Cost

    The most common use for an extension is to remodel or add on a new kitchen. The average kitchen extension cost is £25,000 - £100,000.


    ✔ Can get a kitchen to suit your needs perfectly

    ✔ Can create an open plan kitchen and dining room


    ✖ Can be expensive to replace a kitchen

    Do I Need to Hire an Architect for a Single Storey Extension?

    For most single storey extensions an architect is not necessary. Most experienced builders will be happy to work without one. If, however, you have unusual plans or very specific needs, it can be a good idea to use the services of an architect.

    If you have a set of plans to follow, it means that there is an agreed-upon vision for what the final look of your extension will be. This can also save money in the long run as it will reduce the number of last-minute changes you make.

    Benefits of a Single Storey Extension

    There are several reasons to consider adding an extension to your home. Some of the main benefits are as follows.


    Storage space in a home is always a good thing. When you build an extension, it allows you to add storage that suits your needs perfectly. You can make sure you have the perfect space for anything that is currently cluttering up your living spaces.

    Extra Space

    An extension provides you with more space to live in. For a growing family, this can relieve a lot of tension and make home life more enjoyable.


    Update Home

    Adding an extension is an opportunity to change the feel of your home. You can rearrange the floor plan and make your home work for you. If you have an older property, this is an excellent way to update the space and make it feel more modern.

    Higher Property Value

    The more living space there is in your home, the more it will be worth. By adding an extension to your home, you will increase its value.

    Will Building a Single Storey Extension Increase My Home Value?

    Any work that you do on your home to increase the liveable space will increase the value of your home. With a single storey home, you are trading outdoor space for indoor space. This means the value you add will largely depend on what sort of space you are giving up. If you can build your extension and maintain a reasonable outdoor space, then the value-added will be greater. On average a single storey extension adds around £45,000 to the value of a home.

    Roof Types for Single Storey Extension

    When you get a single storey extension, you have a few options to consider in terms of the roof. The final roof extension cost, and look will play a big part in your decision.

    Pitched Roof Cost


    A pitched roof will allow water to run off and will be in keeping with the rest of your home. There is a range of pitches to choose from. Velux windows can be incorporated if extra light is wanted. The average cost is £9,000 - £15,000.


    ✔ Loft space can be used for storage

    ✔ Long-lasting


    ✖ Not cheap

    Flat Roof Cost

    Flat roofs are an easy to install and cheap option, which makes them popular. The average cost is £5,000 - £8,000.


    ✔ Cheap


    ✖ Lifespan limited to 10-15 years

    ✖ Can fail

    Glazed Roof Cost

    Glazed roofs are a popular choice for side extensions. They are priced per panel of glass at £1,000. If you have a large area of roof, this can easily add up to £10,000 or more.


    ✔ Natural light

    ✔ Striking design feature


    ✖ Expensive

    ✖ Poor insulation

    Green Roof Cost


    Green roofs are ones that have plants growing on them. This can be turf or shrubs. They are an environmentally sound option and provide excellent insulation. The average cost is £100 - £140 per m2. For an average single-story extension, this is around £6,500 - £9,000.


    ✔ Excellent insulation

    ✔ Makes a statement

    ✔ Environmentally friendly


    ✖ Expensive to install

    Building Regulations for Single Storey Extensions

    Building regulations apply to any building work done on a home that makes major changes. This includes extensions. The point of building regulations is to ensure that the building materials and techniques used are safe and up to a minimum standard.

    To get approval from building control, you will need to complete some paperwork and pass a couple of inspections. When they inspect your home, they will look at the whole home, not just the extension. This does mean you may have to update other things in your house, like fire doors, and consumer units.

    The costs cover the paperwork and site visits. You will end up paying £50 - £100 in total. Most contractors will manage the process for you. However, you should make sure it is clear who is taking responsibility for this happening. Ultimately the homeowner is responsible for getting it done.

    Planning Permission for Single Storey Extension

    Before you start any major work on your home, you should check if you need planning permission. Recent changes do mean that a lot more building work is allowed without the need for planning permission, so in most cases, you probably won't need it.

    Do You Need Planning Permission?

    A lot of extensions will be covered under permitted development regulations. The following list identifies the maximum you can do before you need to apply for planning permission

    • A single storey extension on a detached property can extend 4m to the rear. For all other houses, the limit is 3m
    • The maximum height is 4m
    • Any extension should be of the same or similar material as the existing property.
    • You can use no more than half the garden space for the extension.
    • A side extension can be no more than half the width of the original home

    If your planned extension goes beyond these limits, you may need planning permission. Most councils offer a consultation service that will help you identify if you need to apply for planning permission. There is usually a cost of £50 - £150 for this.

    If you live in a conservation area or a national park, then these limits may be smaller.

    Applying for Planning Permission

    If you need planning permission, you can apply through your local council or through the online planning portal. You can make the application yourself, or you can ask your architect or designer to do it for you.

    It costs £206 to apply. You will need to check what documents your local council requires for a submission. Most local councils offer a support service with a small fee. This usually involves a meeting with a council employee. They can guide you through what you need and any potential problems.

    One your application is submitted you will receive confirmation of the application. It will take around 8 weeks for you to get an answer. During this time anyone can lodge objections to your plans. This means it is a good idea to speak to your neighbours about your plans as early as possible. This can prevent issues from arising later on.

    If you are rejected, you can see the reasons why. You can then amend your plans and reapply.

    Alternatives to Single Storey Extension

    If you are looking to increase the space on the ground floor of your home, a single storey extension is not the only option. There are a few other options you might want to consider.

    Prefab Extension Cost

    Prefab extensions are built off-site. They are then moved into position using cranes. They come in a range of materials and finishes. The average cost is £2,000 per m2.


    ✔ Minimal disruption

    ✔ Quick installation


    ✖ Limited options

    ✖ High cost per m2

    Conservatory Cost

    A conservatory is traditionally a mix of glass and brickwork. When it comes to selling your home, it is not considered a liveable indoor space, so adds less value to your home than an extension. There are also limits on the services you can put in a conservatory. The average cost of a conservatory is £15,000.


    ✔ Quick and Easy to Build

    ✔ Cost-Effective


    ✖ Hard to moderate the temperature

    ✖ Less useful than an extension

    Glass Room Cost


    Glass rooms are a little like conservatories but without the brickwork. The glass panels tend to be larger. They are a very modern finish. The average costs are £15,000 - £70,000.


    ✔ Uninterrupted views

    ✔ Modern finish

    ✔ Bespoke


    ✖ Expensive to build

    ✖ Expensive to heat

    Orangery Cost

    Before there were conservatories, there were Orangeries. An Orangery is mainly built from bricks. Traditionally the roof is flat with a raised glass lantern window to allow in light. The average cost is £22,000.


    ✔ Provides more space than a conservatory

    ✔ Provides more light than a traditional extension


    ✖ More expensive than a conservatory

    ✖ The flat roof can require maintenance

    Loft Conversion Cost

    Loft conversions take your existing loft space and turn it into a habitable space. Depending on the scale of the work, you can create a small or large space. There are several choices to make. The average cost of a loft conversion is £40,000. However, a basic loft conversion can cost as little as £15,000.


    ✔ No need to sacrifice outdoor space

    ✔ Good Return on Investment


    ✖ Not an option for all homes

    ✖ Can be expensive to make a usable space

    Cost of Removing a Single Storey Extension

    If your home already has an extension, but you are not happy with it, then you have two options. You can renovate the existing extension, or you can take it down and replace it. To just remove the old extension will cost around £3,000 - £5,000. However, you will need to then replace the old extension with something else. Otherwise, you will just be left with a hole in your house.

    Hiring Single Storey Extension Contractors Checklist

    The contractor you hire for the extension will also be the project manager for the project. Getting the right person for the job is important as there is a lot to coordinate. The wrong person in charge can make the whole project more expensive. Here are some things to look out for.

    • They should be able to show you examples of previous work they have completed.
    • They should be happy to let you speak to previous clients
    • Your contractor should be able to give you a breakdown of the expected costs. Don't expect this on the day. They will likely have to go away and calculate all the costs to give you a realistic quote.
    • A good sign is a contractor who takes notes when you discuss what you want doing. It means that things are less likely to get forgotten about.
    • Check who will be responsible for organising building control visits. Most contractors will do this but make sure it is clearly agreed as it is your responsibility.
    • Check if they are a member of a trade association like the federation of master builders. This is not a guarantee of quality but is a good sign.


    How deep do footings need to be for a single storey extension?
    Footings for s tingle storey extension should be 200mm deep.
    What is a single storey extension?
    A single storey extension is where extra space is added to you home, but only one the ground floor. This can either be done by making existing rooms bigger, or by adding whole rooms joined only by doorways.
    How close to my boundary can I build an extension?
    You can build right up to the boundary of your property. If this is close to your neighbours’ home is advisable to speak to them before you begin building.
    What is the cost of building an extension per square metre?
    The cost per square meter largely depends on the quality of the finish, so you can choose based on your budget. The price ranges between £1,000 - £2,200 per m2.
    Where can I get single storey extension ideas?
    There are plenty of design magazines and self-build website with ideas. It can be good to speak to people who have already built an extension, or view houses with extension to help get ideas for your home.


    Last updated by MyJobQuote on 26th October 2020.

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